As a shock absorber used for effectively absorbing vibration, for instance, a hydraulic shock absorber is widely used in an automobile or the like. The shock absorber is a functional component that plays an important role for vehicle handling, stability and ride quality, especially for ride quality.
Accordingly, there has been proposed a technology for particularly improving ride quality during travel on an expressway by improving friction characteristics of a shock absorber oil composition used in a shock absorber (Patent Literature 1).